A cathode steel bar and a cathode soft belt (CSB) of an electrolytic cell (EC) can be connected by two manners, i.e., welding and compression-joint.
In early designs, pre-baked anode electrolytic cells are all connected by welding at home and abroad, which welding is usually conducted under series power-off condition. For welding of the electrolytic cells of 200 KA or below, some aluminum plants have attempted to use such manners as “shielding”, “draining”, or “direct live welding”. Whether the welding operation is conducted or not is closely related to welder's experience. In addition, even though the welding can be conducted, the welding quality is poorer. In recent years, the size of the electrolytic cell becomes large increasingly, and the rise of current intensity makes bigger the magnetic field intensity around the electrolytic cell, such that the cathode steel bar and the soft belt of a large-sized cell cannot be connected by welding. As such, the cathode steel bar and the cathode soft belt of the electrolytic cell are mostly connected by compression-joint in recent years so as to facilitate overhauling. The advantages and disadvantages of the prior art welding and compression-joint methods are listed as follows:
Compression-jointWeldingImplementingNot requiring series power-offRequiring seriesconditionspower-offConvenienceRelatively troublesome inRelatively troublesomemounting; high requirement onin mounting; requiringcontact surfaces which requirea welding machinepickling, polishing andupon operation formultiple tighteningsurfacing severalsteel platesMaintainabilityPossible, but very troublesomeDifficult tomaintenanceVoltage dropHigher, and usually controlledLower. Usually theunder 20 mvcontrol standard isless than 12 mvThrough-flowPoorer, and greatly influencedGooderuniformityby accidental factors
It can be seen from the above analysis that characteristics of welding exceed or are similar to those of compression-joint except for requirement of series power-off upon operation. Therefore, a technique and related arrangement for live welding of electrolytic cells under series full current is needed to developed, not only to avoid series power-off, but also to reduce the voltage drop of a bus system and facilitate electric balance of the electrolytic cell bus, which brings social and economic benefits of energy saving, production increase and emission reduction to aluminum electrolysis enterprises.